Effects of swirler position on flame response and combustion instabilities

This study is concerned with the experimental and theoretical investigation of the combustion instabilities in a premixed swirl combustor. It is focused on the effects of the swirl mixing distance on the intrinsic thermoacoustic mode. The swirler as an origin of the swirling flow is also the source of the flow disturbance, which has effects on the flame response. The location of the swirler is varied in the experiment to study the effect on combustion instabilities and flame transfer functions. A low order model is built to analyze the thermoacoustic instabilities of the combustion system. The experimental results show that the ITA switches from an unstable state to a stable state as the swirl mixing distance changes with an increment of 15 mm; while the instability of the quarter-wave mode is not varied. The measured Flame Transfer Functions (FTFs) show that the gain curves of the frequency-dependent FTFs seem to be stretched or compressed with the modulation of the swirler position, which has effects on frequencies and instabilities of thermoacoustic modes. With the low order model, the effects of flame response on combustion instabilities are analyzed and the flame dominant nature of the ITA mode is confirmed.